小麦苗期叶片碳氮平衡与低氮诱导的叶片衰老之间的关系

Carbon/Nitrogen Balance Involved in Nitrogen Deficiency Induced Leaf Senescence in Wheat Seedling

为了解小麦叶片衰老与缺氮诱导及碳氮平衡之间的关系,以两个缺氮衰老响应敏感品种(周麦24和运旱618)和两个缺氮衰老响应不敏感小麦品种(衡观35和西农979)为材料,分析了小麦苗期低氮诱导下表征叶片衰老的叶绿素含量、F_v/F_m、净光合速率,以及表征碳氮平衡的全氮和非结构性碳水化合物(可溶性糖、淀粉)比值。结果表明,低氮胁迫后,4个小麦品种叶片的净光合速率、叶绿素含量和F_v/F_m显著降低,说明低氮诱导和加速了小麦叶片的衰老,而缺氮衰老响应敏感品种的衰老程度显著高于不敏感品种。缺氮衰老响应敏感和不敏感小麦品种叶片氮含量在低氮胁迫后均显著降低,同时碳累积量(可溶性糖和淀粉含量)均显著升高。进一步分析表明,缺氮诱导的小麦叶片衰老可能并非受独立的氮缺乏和碳累积调控,而可能与碳氮平衡(碳氮比例)有关,即碳氮平衡可能参与了低氮诱导的叶片衰老调控,而缺氮下耐衰老品种的叶片维持碳氮代谢平衡的能力较强。

Nitrogen deficiency triggers and accelerates the leaf senescence, but the mechanisms are unclear. In order to clarify whether carbon/nitrogen balance is involved in the leaf senescence induced by nitrogen-deficiency, two nitrogen-deficiency sensitive wheat cultivars and two nitrogen-deficiency tolerant wheat eultivars were grown in nitrogen deficient and sufficient solution for 21 days. Leaf senescence was characterized by photosynthesis parameters,chlorophyll content and PSII photochemistry efficiency（Fv/Fm） ,and carbon/nitrogen balance（C/N ratio） of wheat leaf was characterized by the ratio of the non-structural carbohydrates（soluble sugars and starch） content and nitrogen content. The results showed that the net photosynthetic rate,chlorophyll content and Fv/Fm of the four wheat varieties were significantly decreased under nitrogen-deficiency treatment, indicating that nitrogen-defi- ciency induced and accelerated the wheat leaf senescence. The degree of leaf senescence of the nitrogen-deficiency sensitive wheat cultivars was significantly greater than that of the nitrogen-defictency tolerant wheat cultivars. The leaf nitrogen content of all cultivars was decreased,while the non struc tural carbqn carbohydrates content was largely increased under nitrogen-deficiency treatment. There fore,the C/N ratio was increased under nitrogen-deficiency treatment, Further analysis simwed that C/N ratio is highly correlated with the degree of the leaf senescence. The results indicated that the carbon/nitrogen balance is involved in the regulation of nitrogen-deficiency induced leaf senescence, and the wheat cultivars with slightly leaf senescence have stronger capacity to maintain the balance of nitrogen and carbohydrates metabolism,